/*
 * Copyright (C) 2007 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.dx.ssa.back;

import java.util.ArrayList;

import com.android.dx.ssa.SetFactory;
import com.android.dx.util.IntSet;

/**
 * A register interference graph
 */
public class InterferenceGraph {

	/**
	 * {@code non-null;} interference graph, indexed by register in both
	 * dimensions
	 */
	private final ArrayList<IntSet> interference;

	/**
	 * Creates a new graph.
	 * 
	 * @param countRegs
	 *            {@code >= 0;} the start count of registers in the namespace.
	 *            New registers can be added subsequently.
	 */
	public InterferenceGraph(int countRegs) {
		interference = new ArrayList<IntSet>(countRegs);

		for (int i = 0; i < countRegs; i++) {
			interference.add(SetFactory.makeInterferenceSet(countRegs));
		}
	}

	/**
	 * Adds a register pair to the interference/liveness graph. Parameter order
	 * is insignificant.
	 * 
	 * @param regV
	 *            one register index
	 * @param regW
	 *            another register index
	 */
	public void add(int regV, int regW) {
		ensureCapacity(Math.max(regV, regW) + 1);

		interference.get(regV).add(regW);
		interference.get(regW).add(regV);
	}

	/**
	 * Dumps interference graph to stdout for debugging.
	 */
	public void dumpToStdout() {
		int oldRegCount = interference.size();

		for (int i = 0; i < oldRegCount; i++) {
			StringBuilder sb = new StringBuilder();

			sb.append("Reg " + i + ":" + interference.get(i).toString());

			System.out.println(sb.toString());
		}
	}

	/**
	 * Merges the interference set for a register into a given bit set
	 * 
	 * @param reg
	 *            {@code >= 0;} register
	 * @param set
	 *            {@code non-null;} interference set; will be merged with set
	 *            for given register
	 */
	public void mergeInterferenceSet(int reg, IntSet set) {
		if (reg < interference.size()) {
			set.merge(interference.get(reg));
		}
	}

	/**
	 * Ensures that the interference graph is appropriately sized.
	 * 
	 * @param size
	 *            requested minumum size
	 */
	private void ensureCapacity(int size) {
		int countRegs = interference.size();

		interference.ensureCapacity(size);

		for (int i = countRegs; i < size; i++) {
			interference.add(SetFactory.makeInterferenceSet(size));
		}
	}
}
